[IBIS-Users] RE: Role of C_comp

Ling Li,

Regarding: "it has no difference between the simulation on C_comp 0.1pF and 50pF".
That's correct (for the case when the buffer model is driving), and
that's the way HyperLynx 9.0 should also behave.

Thanks,

Arpad
======================================================================

From: Ling Li Ong [mailto:llong@altera.com]
Sent: Wednesday, September 04, 2013 2:19 AM
To: Muranyi, Arpad; ibis-users@eda.org
Cc: Siong Hee Lim
Subject: RE: Role of C_comp

Hi Arpad,

Thanks for your fast response.  I was referring to the mentor's website which commented with using the version 8.2.1, it has no difference between the simulation on C_comp 0.1pF and 50pF.
This version may be outdated compare to latest as I noticed the posting date was on last year.  However, I assume it should perform the same simulation result after this version.
http://communities.mentor.com/mgcx/thread/6935

May I know is this comment align to your understanding?

Thanks.

Regards,
Ling Li

From: Muranyi, Arpad [mailto:Arpad_Muranyi@mentor.com]
Sent: Wednesday, September 04, 2013 2:46 PM
To: Ling Li Ong; ibis-users@eda.org<mailto:ibis-users@eda.org>
Cc: Siong Hee Lim
Subject: RE: Role of C_comp

Ling Li,

It seems that your conclusion from reading Todd Westerhoff's email
in the link you provided is not quite correct.  Todd seems to say
(correctly) that the output waveform of a driver will not change
when C_comp is changed in the IBIS [Model].  You should only see
differences in the waveforms when a reflection hits the driver
and that reflection bounces back off of the driver.  This secondary
reflection from the driver should depend on the C_comp value.

Similarly, if an I/O buffer model is in the receive mode (i.e. input
state), you should see different waveforms when you change the C_comp
value.

As far as I can tell from my days when I worked at Intel and used
HSPICE in my work, HSPICE does what I described above correctly.

Now that I work for Mentor, I can also tell you that the results
of HyperLynx are correct the same way.  I am actually surprised to
hear that you see different results.  Are you sure your test case
is designed well to show and observe these effects correctly?

By the way, the latest HyperLynx version is now 9.0 (not 8.2.1).

I hope this helps answering your question.

Thanks,

Arpad
=======================================================================

From: owner-ibis-users@eda.org<mailto:owner-ibis-users@eda.org> [mailto:owner-ibis-users@eda.org] On Behalf Of Ling Li Ong
Sent: Wednesday, September 04, 2013 12:47 AM
To: ibis-users@eda.org<mailto:ibis-users@eda.org>
Cc: Siong Hee Lim
Subject: [IBIS-Users] Role of C_comp

Hi,

I saw some discussions on c_comp issue at user archive at link:
http://www.eda.org/ibis/users_archive/0487.html

I am confused by the c_comp whether it is double-counted and the different result obtained when using different tools.
According to the comment in the link above, varying the c_comp may see the changes in rise/fall curve.  This is definitely true when using the HSPICE simulator.  But, if you using the latest Hyperlynx  version 8.2.1, changing the c_comp will not reflect the changes in rise/fall curve.

Can you please advise which tools are showing the correct response on c_comp when sweeping at different value?
Thanks.

Regards,
Ling Li






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